全文获取类型
收费全文 | 826篇 |
免费 | 87篇 |
国内免费 | 43篇 |
出版年
2022年 | 6篇 |
2021年 | 18篇 |
2020年 | 7篇 |
2019年 | 7篇 |
2018年 | 7篇 |
2017年 | 15篇 |
2016年 | 17篇 |
2015年 | 20篇 |
2014年 | 37篇 |
2013年 | 37篇 |
2012年 | 43篇 |
2011年 | 40篇 |
2010年 | 33篇 |
2009年 | 35篇 |
2008年 | 32篇 |
2007年 | 40篇 |
2006年 | 42篇 |
2005年 | 34篇 |
2004年 | 34篇 |
2003年 | 44篇 |
2002年 | 32篇 |
2001年 | 32篇 |
2000年 | 37篇 |
1999年 | 20篇 |
1998年 | 8篇 |
1997年 | 22篇 |
1996年 | 8篇 |
1995年 | 21篇 |
1994年 | 5篇 |
1993年 | 15篇 |
1992年 | 13篇 |
1991年 | 15篇 |
1990年 | 13篇 |
1989年 | 16篇 |
1988年 | 7篇 |
1987年 | 15篇 |
1986年 | 5篇 |
1985年 | 15篇 |
1984年 | 6篇 |
1983年 | 9篇 |
1982年 | 8篇 |
1979年 | 7篇 |
1978年 | 5篇 |
1976年 | 6篇 |
1975年 | 6篇 |
1974年 | 6篇 |
1973年 | 7篇 |
1971年 | 10篇 |
1970年 | 5篇 |
1969年 | 7篇 |
排序方式: 共有956条查询结果,搜索用时 196 毫秒
1.
2.
J L Valatx L Paut-Pagano M Fevre-Montange J B Dumas Milne Edwards M Jouvet 《Comptes rendus de l'Académie des sciences. Série III, Sciences de la vie》1992,315(7):295-301
By means of immunocytochemistry, a central neuronal network containing a prolactin-like substance has been described in the rat. In order to demonstrate the synthesis of this peptide in these cells, we examined the presence of prolactin messenger RNA (PRL mRNA) in several brain samples including the pituitary gland. Amplification of the PRL mRNA was performed by the polymerase chain reaction technique, followed by southern blotting and hybridization with a specific oligonucleotide. Results showed the presence of the expected cDNA (468 bp) in the hypothalamus. Another cDNA with a lower molecular weight was also observed. 相似文献
3.
The quality of Cucurbita pepo L. pollen was studied using field pollinations and the fluorochromatic-reaction test. The extreme sensitivity of this pollen to dehydration and ageing is demonstrated. Controlled stress applied to mature pollen leads to the development of seedless fruits. Molecular signals seem to be involved in the induction of this parthenocarpy. These results indicate the existence of distinct sequences involved in the completion of the fertilization program of pollen. With pollen altered by stress, the fertilization process may be stopped at different stages of its completion. We bring evidence that Cucurbita pepo plants have developed special adaptations in order to compensate for the poor viability of their pollen.Abbreviation FCR
fluorochromatic reaction 相似文献
4.
The posterior ligaments: ligamentum flavum, articular, interspinous and supraspinous ligaments of twenty five fresh cadaveric intervertebral segments, from T11-T12 to L4-L5, extracted from fourteen spines were tested in tension. A progressive dissection method was used, that is, each segment was tested after first resecting the disk with the ligaments intact and a force-elongation curve obtained. Then one ligament was cut and the test repeated, and so on. The most restrictive ligament was found to be the ligamentum flavum followed by the articular, interspinous, and supraspinous ligaments. 相似文献
5.
Catherine Digonnet-Kerhoas Gilles Gay Jean Claude Duplan Christian Dumas 《Planta》1989,179(2):165-170
During ageing of the short-lived pollen grains of Cucurbita pepo L., water loss was examined in relation to viability using biophysical (1H-nuclear magnetic resonance, NMR) and cytological methods (fluorochromatic reaction test, freezefracture and scanning electron microscopy). A semi-logarithmic representation of the pollen weight loss demonstrated the complexity of the dehydration process. A the study of proton loss using 1H-NMR indicated that two major releases water of had taken place, each with different flux rates. Pulse 1H-NMR experiments showed the occurrene of non-exponential signal decay as a function of time, indicating the existence of different fractions of water in a pollen grain sample. These fractions leave the pollen grain at different times during pollen dehydration, and one of them (that of the so-called vital water) can be related to pollen viability. The quantity of protons giving a signal during pulse 1H-NMR experiments was very low when the pollen grains were judged to be dead according to the fluorochromatic test. Freeze-fracture replicas of these dead pollen grains (less than 25% water content) showed that the plasma membrane had become detached from the intine surface; this ultrastructural feature might therefore be involved in the loss of pollen viability.Abbreviations A
initial amplitude of the NMR signal
- A2
quantity of water charcterized by T2-2
- A5
quantity of water characterized by T2–5
- FCR
fluorochromatic reaction
- NMR
nuclear magnetic resonance
- T2
transverse relaxation time
- T2-2
T2 measured with 2 ms between each pulse of radiofrequency
- T2–5
T2 measured with 5 ms between each pulse of radiofrequency 相似文献
6.
Intercellular fluid (IF) extracted from the apoplastic leaf spaces of Petunia contained up to 6 new soluble proteins, called d proteins (d0 to d5). Characterisation of the d proteins has shown that they can be divided into groups and show a genetic variability similar to the PR(b) proteins from Nicotiana. d protein patterns from Petunia interspecific hybrids clearly show that the determinant for the d proteins in sexually transmitted as is the case for b proteins in Nicotiana. d-protein induction in TMV-SM1 infected Petunia leaves is discussed in relation to the resistance to infection shown by cultivars and hybrids of Petunia. 相似文献
7.
Summary An attempt was made to transfer two sorts of DNA into maize via pollen grains. Controls for both pollen quality and DNA behaviour during the transformation experiments were included. When genomic DNA was used, no transformants were observed among the 1805 seeds screened. With plasmid DNA (harbouring the gene expressing kanamycin resistance in plant cells), three plants with kanamycin resistance were observed among the 1723 seeds screened, although no molecular evidence of transformation was obtained. Experiments indicated that under the conditions used, DNA was being degraded by both pollen and stigma nucleases. Consequently, we attempted to determine protocols which would inhibit these nuclease activities in order to preserve DNA integrity during transformation experiments, thus allowing fertilization. We found that a classic germination medium supplemented by 300 or 600 mM KNO3, or 20% PEG1550 satisfied all these conditions.Abbreviations BK
Brewbaker and Kwack medium
- BKS15
Brewbaker and Kwack medium containing 15% (w/v) sucrose
- EDTA
ethyldiaminetetraacetic acid
- FCR
fluorochromatic reaction
- FP
fertilization percentage
- PEG
polyethylene-glycol 相似文献
8.
Summary In mature viable pollen ofBrassica oleracea, the pair of sperm cells and the nucleus of the vegetative cell are linked to form a structured unit we term the male germ unit. The sperm cells are held within a common periplasm and have no cell walls. Each sperm cell has a central globular body containing the nucleus surrounded by several evaginations which provide the means for linkage between them. One sperm cell, usually that closest to the nucleus of the vegetative cell contains most of mitochondria profiles (plastids are absent). This sperm cell appears to be linked by its protoplasmic evaginations to the envelope of the vegetative nucleus. The role of this unit in interactions with the female gametic complex is considered. 相似文献
9.
The respiration of insects at reduced pressures II. The uptake of oxygen by Tenebroides mauritanicus
The respiration of larvae of Tenebroides mauritanicus exposed to reduced pressures in air was measured in a specially designed chamber by means of gas chromatography. Both O2 uptake and CO2 output were progressively reduced as the pressure was lowered from 200 to 35 mm Hg. There were differences in the amounts of gases exchanged when the insects were exposed under dry or moist conditions. When expired CO2 was allowed to accumulate, in some experiments it had a marked stimulating effect on O2 uptake between 60 and 200 mm. The respiratory quotient at the various pressures was calculated and the values found under different conditions of pressure and moisture are discussed.
In this paper pressures are given as absolute pressures expressed in mm Hg. 相似文献
Zusammenfassung In der ersten Veröffentlichung dieser Reihe beschrieben Monro, Dumas und Buckland (1962) die Kohlendioxyd-Ausatmung der Larven von T. mauritanicus bei verringertem atmosphärischen Druck. Unter 65 mm nahm die CO2-Ausatmung deutlich und fortschreitend ab. Um zu zeigen, daß dieser Verringerung der CO2-Produktion tatsächlich eine Abnahme der Atmung entspricht, wurde ein Apparat entwickelt, mit dessen Hilfe O2-Aufnahme und CO2-Abgabe der Insekten gaschromatographisch gemessen werden konnten.Bei dreistündiger Exposition wurde unter den experimentellen Bedingungen gefunden, daß sich im Vergleich mit der Reaktion bei höherem Druck sowohl O2-Aufnahme als auch CO2-Abgabe bei 100, 60 und 30 mm fortschreitend verringert. Bei so niedrigem Druck war die Atmung während der Expositionszeit gleichmäßiger als bei höherem Druck, bei dem von Zeit zu Zeit deutliche Schwankungen auftraten. Bemerkenswert war ein deutlicher Unterschied in der Respirationsrate bei feuchtigkeitsgesättigter Luft und unter trockenen Bedingungen. Bei hoher Luftfeuchtigkeit war die O2-Aufnahme zwischen 100 und 400 mm größer als bei Trockenheit und die CO2-Abgabe war größer von 65 mm aufwärts. Daraus wird gefolgert, daß in diesem Druckbereich bei Trockenheit der Austausch beider Gase durch dauernden oder zeitweisen Verschluß der Atmungswege behindert wird.In einigen Versuchen wurde CO2 durch Absorption aus der die Insekten umgebenden Atmosphäre entfernt. Abwesenheit von CO2 verringerte die O2-Aufnahme im Bereich von 60–200 mm besonders bei Feuchtigkeit. Bei Trockenheit war die O2-Aufnahme bei hohem CO2-Gehalt signifikant geringer. Hier mag wiederum Schließung der Atmungswege die stimulierende Wirkung des CO2 vermindert haben.Berechnungen des Respirationsquotienten aus den verfügbaren Daten zeigen eine stetige Abnahme dieses Wertes mit abnehmendem Druck bei Feuchtigkeit, während der R.Q. in trockener Umgebung bei jedem Druck ziemlich konstant blieb. Es werden keine endgültigen Schlüsse aus diesen Berechnungen gezogen, aber es wird angenommen, daß die feuchte Umgebung einen freieren Gasaustausch durch die Atmungswege erlaubt und daher bessere Bedingungen zur Bestimmung des tatsächlichen R.Q.-Wertes bei vermindertem Druck bietet.
In this paper pressures are given as absolute pressures expressed in mm Hg. 相似文献
10.
The effects of ethylene and of indole-3-acetic acid (IAA) on growth of excised pea root sections have been compared under a variety of conditions. After 16 hours treatment the inhibitory action of IAA is fully reversible on transfer of the root sections to IAA-free solutions. In contrast, inhibition by ethylene is almost totally irreversible. IAA inhibits growth from zero time; ethylene is generally without effect during the first 3 to 6 hours. The inhibitory action of ethylene is dependent on factors such as tissue age and solution composition which have no major effect on IAA inhibition. Ethylene production is enhanced by 100 μm IAA, but conditions which reduce the rate of ethylene evolution 2 to 3-fold at the same IAA concentration fail to affect the inhibitory action of IAA on elongation. It seems unlikely that ethylene can play more than a minor role in mediating inhibition of pea root growth by IAA. 相似文献